Geol 151 – Geomorphology Fall 2008 Your Name_________________________ Survey Partners_________________________ _________________________ _________________________ Fluvial Terrace on the Huntington River – Deglacial and Post-glacial History of Northern Vermont Fig 5.2 from Whalen, 1998. Schematic evolution of valley formation Introduction: We will return to the Huntington River Audubon Center this week to learn how to rapidly survey (using Pop-Levles) a flight of fluvial terraces formed during the deglacial and post-glacial history of the Huntington and Winooski River valleys, Vermont. In addition to these fast surveys, we will construct more detailed cross-sections of several fluvial features and terrace risers (scarps) cut into floodplains abandoned by the Huntington River during the Holocene using instruments called Auto-Levels. Finally, we will place the data we collect in the context of a pre-existing and comprehensive body of work assembled by Tim Whalen in 1998 in order to understand better how the landscape we tread upon today was created in the past through the actions of ice, falling levels of pro- glacial lakes, flowing water, changing climate, and the activities of humans over the past 200 years. What to hand in: This handout with all questions answered, your Pop Level and Auto Level field sketches drawn to scale, an excel plot of your auto-level cross-section (Completed by end of class on Friday), and your concept sketches of the Huntington River longitudinal profiles. 1 Geol 151 – Geomorphology Fall 2008 Gear we will need: • 5 GPS units • 5 of each the ortho and topo laminated maps. • 5 pop levels • 100 m, and several 30 m tapes. • 5 auto levels, tripods, and stadia rods. • Extras: extra batteries, cameras. Specific Skills and Knowledge: By the end of this week’s lab, you should be comfortable with the following items: • Collecting GPS points at the beginning and ending of both your Pop-Level and Auto-Level surveys. • Collecting fast survey data using a Pop-Level and stadia rod. • Collecting detailed survey data using an Auto-Level, tripod, and stadia rod. • Plotting field sketches to scale. • Plotting and analyzing your more detailed surveys of river meanders and terrace risers. • Placing all of your findings in context of Tim Whalen’s work studying Huntington River terraces, particularly longitudinal profiles. • Contemplating how the Huntington River Gorge, located downstream of the terraces we surveyed fits into the evolution of the Huntington River Valley. We will park at the Sugarhouse parking lot, and begin our lab with a short practice session using pop levels and stadia rods to survey a landscape as opposed to a river channel. Groups will then use these techniques to survey from the terrace scarp behind the peeper pond down to the Huntington River channel. There we will regroup as a class and go through the basics of surveying with an auto level. Groups will again split off and construct detailed cross-sections. Two groups will survey an abandoned meander, while the other three will survey terrace risers increasing in age to detect changes in slope. Field Task 1 - Collecting GPS readings at the beginning and ending of your pop-level survey: Collect a GPS reading at the first and last point of your terrace survey. This will enable you to see the angle of the trajectory you walked in relation to the active river channel on the grided laminated maps. Beginning GPS point _______________Easting______________Northing________Elev Ending GPS point _______________Easting______________Northing________Elev 2 Geol 151 – Geomorphology Fall 2008 Field Task 2 - Conducting your Pop-Level Survey: (Gear you will need: GPS unit and maps, Pop level, stadia rod.) Break up into 5 groups. Now get organized such that one person is the designated pop- leveler, one person holds the stadia rod, one person is the data collector and one person is the field sketcher. Refer to the pop level data collection sheet…it has many helpful hits regarding how to collect your data. 1) The first thing you need to do is figure out how many paces it takes for the person with the stadia rod to walk 30 meters. This way you approximate the distance between your points simply by counting how many paces it takes to walk to the next one. Stretch a 30 meter take out along the ground and have the person holding the stadia rod casually stride from beginning to end. Record how many paces it took. Now divide 30 meters by the number of paces and you have a measure of Meters Per Pace (MPP). Record this on your data sheet. It will be used to calculate all of your distances. 2) Have the person with the pop level stand directly in front of the stadia rod such that the pop levelers feet and the bottom of the rod are at exactly the same level. Record the height that the pop levelers see on the data sheet. This is the eye level of the pop level and will be used to calculate all elevation changes between points. 3) Have the pop leveler stand at the uppermost position of your cross-section. This is your starting position and first point. After using the data sheet to calculate, both your distance and height should be zero. 4) Now have the person with the stadia rod walk down hill to the next point, counting paces as he or she goes. Record the number of paces on the datasheet and immediately calculate the distance the rod person has walked and record. 5) Now, while the person with the stadia rod is standing at this point, have the pop leveler site the level they read on the rod and record this value on the datasheet. The Height of the Pop Leveler (HPL) minus the new height seen on the stadia rod will yield the elevation difference between the original point and the surveyed point. Note that because your first point is at a height of zero, and we are walking downhill, the height of every subsequent point will be negative. 6) Repeat these steps until you have surveyed down to the water’s edge. You want to choose your points carefully such that you catch all major breaks in slope. Your point spacing will depend heavily upon how sloped the ground surface is. If the surface is flat, you probably only need a couple of points to characterize it. If the ground pitches steeply, you’ll want more survey point sand you will want them at the inflections. 7) Remember that all the while, the field sketcher must be constructing a cross- section field sketch draw to scale. You will hand this in, so make it neat. You can include any relevant information on it that you think is useful. Later in the lab, you will be asked to think about how much of the total height of terraces you just surveyed. Below, record the total elevation change in meters. If your beginning height is zero, and your ending height is -35.1 meters, your total elevation change is 35.1 meters. Total elevation change = ____________________meters 3 Geol 151 – Geomorphology Fall 2008 Field Task 3 - Conducting your Auto-Level Survey: (Gear you will need: Auto-Level, Tripod, and Stadia Rod) After completing a rough survey of terraces, we will conduct a much more detailed survey of subtle geomorphic features using Auto-Levels. This will allow us to measure more accurately changes in height and distance, and allow us to visualize and quantify changes in shape and slope of the landscape. Which feature is your group surveying? _____________________________________ (Either the channel meander, the oldest riser, the middle riser, or the youngest riser) 1) Get yourselves organized again. During the surveying, try and let everyone take a turn with all parts of the operation. For starters, designate one person as the auto leveler, one person as the stadia rod holder, one person as the data recorder, and one person as the field sketcher. 2) Take some time and familiarize yourselves with the data collection sheet. If used correctly, you will wind up with perfect X –Y coordinate pairs that you won’t need to change at all when you get back to the computer lab. 3) First thing to do is measure the Instrument Height (IH) and record it on your datasheet. It will be used to calculate all elevations. Measure from the ground surface up to the eyepiece of the auto level mounted on the tripod. It should be set up so you can comfortably look through the instrument without bending over too far. 4) Measuring Distance: record both the reading of the top and bottom stadia lines on your collection sheet. By subtracting the bottom from the top, then multiplying by 100, you will get the distance that the stadia rod is away from the auto level. This is your X coordinate. All but one of the stadia rods are in meters. The group with the rod in decimal feet, make sure to talk to us before beginnging your survey. 5) Measuring Height: record the reading at the center of the crosshairs. By subtracting the Instrument Height from this value, you will get the height above or below the ground surface where the auto level is set up. This is your Y coordinate. 6) Make sure that the field sketcher is constructing an accurate sketch as you go from point to point. It is much easier to spot a mistake in your sketch than in a table of numbers. 7) If you are surveying the meander, make sure to survey all the way from the instrument, across the paleochannel, and up the adjacent terrace scarp as high as you can go (either until you are blocked by foliage, or the auto leveler can no longer see the bottom of the stadia rod).